Coriolis mass measuring device

ABSTRACT

A Coriolis mass flow measuring device includes a vibratory measuring transducer having at least one measuring tube, which has medium flowing through it during operation. In operation, the measuring tube is caused by an exciter arrangement to undergo mechanical oscillations, especially bending oscillations. Additionally, the Coriolis mass flow measuring device includes a sensor arrangement for producing oscillation measurement signals (s 1 , s 2 ) representing the inlet-end and outlet-end oscillations of the measuring tube. Measuring device electronics controlling the exciter arrangement produces an exciter current (i exc ) and an intermediate value (X′ m ) derived from the oscillation measurement signals (s 1 , s 2 ). This intermediate value represents an uncorrected mass flow. Derived from the exciter current and/or from a component of the exciter current (i exc ), an intermediate value (X 2 ) is produced, which corresponds to a damping of the oscillations of the measuring tube. This damping is especially a function of an apparent viscosity, and/or a viscosity-density product, of the medium guided in the measuring tube. Furthermore, a correction value (X K ) is produced for the intermediate value (X′ m ) utilizing the intermediate value (X 2 ) and a viscosity measurement value (X η ) determined initially or during operation. The viscosity measurement value (X η ) corresponds to a viscosity of the medium guided in the measuring tube and/or to a predetermined reference viscosity. On the basis of the intermediate value (X′ m ) and the correction value (X K ), the measuring device electronics then produces an exact mass flow rate measurement value (X m ).

This is a continuation of U.S. application Ser. No. 11/084,507 filed onMar. 21, 2005 now U.S. Pat. No. 7,040,181 which is a nonprovisional ofprovisional application No. 60/556,491 filed on Mar. 26, 2004 andprovisional application No. 60/570,490 filed on May 13, 2004.

FIELD OF THE INVENTION

The invention relates to a Coriolis mass flow/density meter for amedium, particularly a medium of two or more phases, flowing in apipeline, as well as to a method for producing a measurement valuerepresenting mass flow.

BACKGROUND OF THE INVENTION

In the technology of process measurements and automation, for themeasurement of physical parameters of a medium flowing in a pipeline,parameters such as e.g. mass flow rate, density and/or viscosity, it iscommon to use such in-line measuring devices, especially Coriolis massflow measuring devices, which use a vibratory transducer inserted intothe course of the pipeline conducting the medium and traversed by themedium during operation, and a measuring and operating circuit connectedthereto, to produce reaction forces in the medium, forces such as e.g.Coriolis forces related to the mass flow rate, inertial forces relatedto the density, and frictional forces related to the viscosity, etc.,and to derive from these one or more measurement signals representingthe current mass flow rate, the current viscosity and/or the currentdensity of the medium. Such in-line measuring devices having a vibratorytransducer, as well as the way in which they operate, are known per seto those skilled in the art and are described extensively and in detaile.g. in WO-A 03/095950, WO-A 03/095949, WO-A 03/076880, WO-A 02/37063,WO-A 01/33174, WO-A 00/57141, WO-A 99/39164, WO-A 98/07009, WO-A95/16897, WO-A 88/03261, EP-A 1 281 938, EP-A 1 001 254, EP-A 553 939,US 2003/0208325, or the U.S. Pat. Nos. 6,691,583, 6,651,513, 6,513,393,6,505,519, 6,006,609, 5,869,770, 5,796,011, 5,602,346, 5,602,345,5,531,126, 5,301,557, 5,253,533, 5,218,873, 5,069,074, 4,876,898,4,733,569, 4,660,421, 4,524,610, 4,491,025, or 4,187,721.

It is noted that the transducers are also sometimes referenced in theliterature as sensors. The term “transducer” is used here, because aherein-discussed component of the transducer also bears the label“sensor”.

For guiding the medium, the transducers include always at least onemeasuring tube held, for example, in a tubular or box-shaped supportframe. The measuring tube has a curved or straight tube segment, whichis caused to vibrate—driven by an electromechanical exciterarrangement—during operation for producing the above-mentioned reactionforces. For registering vibrations, particularly vibrations at the inletand outlet ends, of the tube segment, the measuring transducersadditionally have electrophysical sensor arrangements reacting tomovements of the tube segment. With Coriolis mass flow measuring devicesfor a medium flowing in a pipeline, the measuring of the mass flow rateis accomplished, for example, by allowing the medium to flow through themeasuring tube interposed in the pipeline and oscillating the tubeduring operation, whereby the medium experiences Coriolis forces. Theseforces, in turn, effect that the inlet and outlet regions of themeasuring tube oscillate with phases which are shifted with respect toone another. The size of this phase shift serves as a measure for themass flow rate. Then the oscillations of the measuring tube areregistered by means of two oscillation sensors of the above-mentionedsensor arrangement separated from one another along length of themeasuring tube and are transformed into oscillation measurement signals,from whose mutual phase difference the mass flow rate is derived.

Already the above-referenced U.S. Pat. No. 4,187,721 mentions that alsothe instantaneous density of the flowing medium is usually measurablewith Coriolis mass flow measuring devices, and, indeed, on the basis ofa frequency of at least one of the oscillation measurement signalsdelivered by the sensor arrangement. Moreover, usually a temperature ofthe medium is also measured directly, in suitable manner, for instanceby means of a temperature sensor arranged on the measuring tube. Besidesthe mass flow rate and/or the density of the medium, Coriolis mass flowmeasuring devices or other in-line measuring devices with a vibratorytransducer can also be used to measure a viscosity and/or aviscosity-density product of the medium flowing in the measuring tube;see, in this connection, particularly the U.S. Pat. Nos. 6,651,513,5,531,126, 5,253,533, and 4,524,610, or WO-A 95/16897. It can thus beassumed, without more, that, even when not expressly described, modernin-line measuring devices with a vibratory measuring transducer,especially Coriolis mass flow measuring devices, enable measurement alsoof density, viscosity and/or temperature of the medium, especiallyconsidering that these measurements can, in any case, always be used forcompensation of measurement errors resulting from fluctuating mediumdensity and/or medium viscosity; see, in this connection, especially thealready mentioned U.S. Pat. Nos. 6,513,393, 6,006,609, and 5,602,346, aswell as WO-A 02/37063, WO-A 99/39164, and WO-A 00/36379.

In the application of vibratory transducers, it has, however, beenfound, as also discussed, for instance, in JP-A 10-281846, WO-A03/076880, and U.S. Pat. No. 6,505,519, that, in the case ofinhomogeneous media, especially media of two or more phases, theoscillation measuring signals derived from the oscillations of themeasuring tube, especially the mentioned phase shift, are subject tofluctuations to a considerable degree, in spite of keeping viscosity anddensity of the separate phases, as well as the mass flow rate, constantand/or appropriately taking them into consideration, such that, withoutremedial measures, the signals can become completely unusable formeasuring the desired physical parameter. Such inhomogeneous media can,for example, be liquids, into which, as e.g. practically unavoidable indosing- or bottling-processes, gas, especially air, present in thepipeline, is entrained, or from which a dissolved medium, e.g. carbondioxide, outgases and leads to foam formation. Other examples of suchinhomogeneous media are emulsions, as well as wet, or saturated, steam.In terms of causes for the problems experienced in the measurement ofinhomogeneous media by means of vibratory transducers, one can mention,for example, the unilateral attachment or deposition of gas bubbles orsolids particles internally on the wall of the measuring tube, and theso-called “bubble-effect”, in which entrained gas bubbles act as flowguides for liquid volume elements accelerated transversely to themeasuring tube longitudinal axis.

While a flow, or medium, conditioning, as the case may be, preceding theactual flow measurement is proposed in WO-A 03/076880 for lessening themeasurement errors associated with media of two or more phases, JP-A10-281846 and, also, U.S. Pat. No. 6,505,519, each describe a correctingof the flow measurement, especially mass flow rate measurement, based onoscillation measurement signals, particularly using an evaluation ofshortfalls between a highly accurately measured, actual medium densityand an apparent medium density determined during operation by means ofCoriolis mass flow measurement devices.

In particular, pre-trained, occasionally even adaptive, classifiers ofthe oscillation measurement signals are proposed for this purpose. Theclassifiers can be constructed, for example, in the form of a Kohonenmap or a neural network, and can perform the correction either on thebasis of a few parameters measured during operation, especially the massflow rate and the density, along with further characteristics derivedtherefrom, or also by using an interval of the oscillation measurementsignals encompassing one or more oscillation periods. The use of suchclassifiers has, for example, the advantage, that, in comparison toconventional Coriolis mass flow/density meters, no, or only very slight,changes have to be made at the transducer, be it with respect to themechanical construction, the exciter arrangement, or the operatingcircuit controlling such, which are adjusted to accommodate the specialapplication. However, there is a significant disadvantage of suchclassifiers, among other things, in that, compared to conventionalCoriolis mass flow measuring devices, considerable changes are requiredin the realm of measurement value production, especially as regards theanalog-to-digital converters and the microprocessors which are used.Thus, as described in the U.S. Pat. No. 6,505,519, such signalevaluation requires, for example in the digitizing of the oscillationmeasurement signals, which can have an oscillation frequency of around80 Hz, a sampling rate of about 55 kHz, or more, in order to achievesufficient accuracy. Said differently, the oscillation measurementsignals must be sampled using a sampling ratio significantly above600:1. On top of this, also the firmware stored and executed in thedigital measuring circuit becomes correspondingly complex. An additionaldisadvantage of such classifiers is to be seen in the fact that theymust be trained and correspondingly validated for the measuringconditions actually present during operation of the transducer, be itthe conditions of installation, the medium to be measured, and itsusually variable properties, or other factors affecting the accuracy ofmeasurement. Due to the high complexity of the interactions of all thesefactors, the training and its validation can finally usually only bedone at the site and individually for each transducer, this, in turn,leading to a considerable expense being associated with the start-up ofthe transducer. Finally, it has also been found, that suchclassification algorithms, on the one hand because of the greatcomplexity, and, on the other hand, because of the fact that, usually, acorresponding mathematical physics model with technically relevant orunderstandable parameters is not explicitly present, classifiers exhibita very low transparency and are, consequently, often difficult to place.Accompanying this, considerable resistance can arise with customers,with such acceptance problems especially occurring when it concernsclassifiers involving a self-adapting mechanism, for instance a neuralnetwork.

As another possibility for avoiding the problem with inhomogeneousmedia, U.S. Pat. No. 4,524,610 proposes, for example, to install thetransducer such that the straight measuring tube extends essentiallyvertically, in order to prevent, as much as possible, an attachment ofsuch interfering, especially gaseous, inhomogeneities. This is, however,a very special solution which cannot always be realized, without more,in industrial process measurement technology. On the one hand, thepipeline, into which the transducer is to be inserted namely for thiscase, must, on occasion, be fitted to the transducer, and not thereverse, a fact which can mean increased extra expense to the user increating the measurement location. On the other hand, the measuringtubes can, as already mentioned, be curved, so that the problem cannotalways be satisfactorily solved by an adjustment of orientation in theinstallation. It has also been found, in this connection, that thementioned corruptions of the measurement signal cannot necessarily beavoided with certainty by the use of a vertically installed, straightmeasuring tube.

SUMMARY OF THE INVENTION

An object of the invention is to provide a corresponding Coriolis massflow measuring device that is suited for measuring mass flow rate veryaccurately, even in the case of inhomogeneous media, especially media oftwo or more phases, and, indeed, preferably with a measurement error ofless than 10% referenced to the actual mass flow rate. A further objectis to provide a corresponding method for producing a corresponding massflow rate measurement value.

For achieving this object, the invention provides a Coriolis mass flowmeasuring device, especially a Coriolis mass flow/density measuringdevice, or a Coriolis mass flow/viscosity measuring device, formeasuring the mass flow rate of a medium flowing in a pipeline,especially a medium of two or more phases, which Coriolis mass flowmeasuring device includes a vibratory transducer and a measuring deviceelectronics electrically coupled to the transducer,

-   -   wherein the transducer has:        -   at least one measuring tube to be interposed in the            pipeline, especially an essentially straight measuring tube,            for guiding the medium to be measured and communicating with            the connected pipeline,        -   an exciter arrangement acting on the measuring tube for            causing the at least one measuring tube to vibrate with            bending oscillations at least at times, and/or at least in            part, during operation, as well as        -   a sensor arrangement for registering vibrations of the at            least one measuring tube, which delivers at least one, first            oscillation measurement signal representing oscillations of            the measuring tube at the inlet end and at least one, second            oscillation measurement signal representing oscillations of            the measuring tube at the outlet end, and    -   wherein the measuring device electronics        -   delivers, at least at times, an exciter current driving the            exciter arrangement and, at least at times, a mass flow rate            measurement value representing a mass flow rate to be            measured,        -   produces a first intermediate value derived from the            oscillation measurement signals and corresponding to the            mass flow rate to be measured and/or to a phase difference            between the two oscillation measurement signals, as well as            a second intermediate value derived from the exciter            current, and/or from a component of the exciter current, and            corresponding to a damping of the oscillations of the            measuring tube, especially a damping dependent on an            apparent viscosity, and/or a viscosity-density product, of            the medium guided in the measuring tube, as well as        -   uses the second intermediate value and a viscosity            measurement value predetermined, or determined during            operation, especially by use of the transducer and/or the            measuring device electronics, and corresponding to a            viscosity of the medium guided in the measuring tube and/or            to a previously supplied, reference viscosity, to produce a            correction for the first intermediate value, and, on the            basis of the first intermediate value and the correction,            the mass flow rate measurement value.

Additionally, the invention resides in a method for measuring a massflow rate of a medium, especially a medium of two or more phases,flowing in a pipeline, using a Coriolis mass flow measuring devicehaving a vibratory transducer and a measuring device electronicselectrically coupled with the transducer, which method includes thefollowing steps:

-   -   flowing the medium to be measured through at least one measuring        tube of the transducer communicating with the pipeline and        feeding an exciter current into an exciter arrangement        mechanically coupled with the measuring tube guiding the medium        for causing mechanical oscillations of the measuring tube,        especially bending oscillations,    -   letting the measuring tube vibrate in an oscillation mode suited        for producing Coriolis forces in the medium flowing        therethrough,    -   registering vibrations of the measuring tube and producing a        first oscillation measurement signal representing inlet-end        oscillations and a second oscillation measurement signal        representing outlet-end oscillations,    -   developing, using the two oscillation measurement signals, a        first intermediate value corresponding to the mass flow rate to        be measured and/or to a phase difference between the two        oscillation measurement signals,    -   determining a second intermediate value derived from the exciter        current and corresponding to a damping of the oscillations of        the measuring tube dependent on an apparent viscosity, and/or a        viscosity-density product, of the medium guided in the measuring        tube,    -   producing a correction value for the first intermediate value by        means of the second intermediate value and by means of an        initially determined viscosity measurement value, especially by        use of the transducer and/or the measuring device electronics,        corresponding to a viscosity of the medium guided in the        measuring tube, as well as    -   correcting the first intermediate value by means of the        correction value and producing a mass flow rate measurement        value representing the mass flow rate to be measured.

In a first development of the Coriolis mass flow measuring device of theinvention, the correction value represents a deviation of the viscosityof the medium from an apparent viscosity of the medium guided in themeasuring tube, determined during operation on the basis of the excitercurrent and/or a component of the exciter current, and/or from aviscosity-density product of the medium guided in the measuring tube,determined during operation on the basis of the exciter current.

In a second development of the Coriolis mass flow measuring device ofthe invention, the measuring device electronics determines thecorrection value on the basis of a comparison of the second intermediatevalue with the viscosity measurement value and/or on the basis of adifference existing between the second intermediate value and theviscosity measurement value.

In a third development of the Coriolis mass flow measuring device of theinvention, the measuring device electronics produces the secondintermediate value also using at least one of the oscillationmeasurement signals.

In a fourth development of the Coriolis mass flow measuring device ofthe invention, the exciter arrangement causes the measuring tube toexecute torsional oscillations during operation at least at times and/orat least in part, especially torsional oscillations alternating with thebending oscillations, or superimposed over time on the bendingoscillations, about an imaginary longitudinal axis of the measuring tubeessentially aligned with the measuring tube, especially a principle axisof inertia of the measuring tube, and the measuring device electronicsdetermines also the viscosity measurement value on the basis of theexciter current driving the exciter arrangement and/or on the basis of acomponent of the exciter current.

In a fifth development of the Coriolis mass flow measuring device of theinvention, the measuring tube, driven by the exciter arrangement,executes torsional oscillations having a measuring tube torsionaloscillation frequency arranged to be different from a measuring tubelateral oscillation frequency with which the measuring tube, driven bythe exciter arrangement, executes lateral oscillations, especiallybending oscillations.

In a sixth development of the Coriolis mass flow measuring device of theinvention, the measuring device electronics also produces the viscositymeasurement value.

In a seventh development of the Coriolis mass flow measuring device ofthe invention

-   -   the measuring device electronics delivers a density measurement        value derived from the first and/or the second oscillation        measurement signal and representing a density of the medium, and    -   the measuring electronics determines the correction value,        especially the viscosity measurement value, also on the basis of        the density measurement value.

In an eighth development of the Coriolis mass flow measuring device ofthe invention, the measuring device electronics is coupled with anexternal viscosity measurement device, especially a viscosity measuringdevice located remotely from the Coriolis mass flow measuring device,and the viscosity measurement device delivers the viscosity measurementvalue at least at times.

In a ninth development of the Coriolis mass flow measuring device of theinvention, the measuring device electronics is coupled, at least attimes, with a differential pressure sensor, which, at least at times,delivers a differential pressure measurement value representing apressure difference over a length of the pipeline.

In a tenth development of the Coriolis mass flow measuring device of theinvention, the measuring device electronics determines, at least attimes and on the basis of the exciter current and/or on the basis of acomponent of the exciter current, as well as with the use of theviscosity measurement value, a concentration measurement value, whichrepresents a volume, and/or mass, fraction, especially a relativevolume, and/or mass, fraction, of a phase in a two- or more-phase mediumin the measuring tube.

In an eleventh development of the Coriolis mass flow measuring device ofthe invention, the measuring tube communicates with the connectedpipeline through an inlet fitting opening into an inlet end and anoutlet fitting opening into an outlet end, and the transducer includes,fixed at the inlet and outlet ends of the measuring tube, especiallymechanically coupled with the exciter arrangement, a counter-oscillator,which vibrates at least at times during operation, especially with phaseopposite to that of the measuring tube.

In a twelfth development of the Coriolis mass flow measuring device ofthe invention, the Coriolis mass flow measuring device is used formeasuring a mass flow of a two- or more-phase medium flowing in apipeline, especially a liquid-gas mixture.

In a first development of the method of the invention, the methodfurther includes the step of actuating bending oscillations in themeasuring tube for producing Coriolis forces in the medium flowingthrough the measuring tube.

In a second development of the method of the invention, the methodfurther includes the step of actuating torsional oscillations in themeasuring tube, especially torsional oscillations superimposed on thebending oscillations, as well as the step of determining a secondintermediate value on the basis of the exciter current and/or at least acomponent of the exciter current actuating the torsional oscillations ofthe measuring tube.

In a third development of the method of the invention, the step ofproducing the correction value for the intermediate value furtherincludes the step of comparing the second intermediate value with theviscosity measurement value and/or determining a difference between thesecond intermediate value and the viscosity measurement value, as wellas the step of determining a deviation of the viscosity of the mediumfrom an apparent viscosity of the medium guided in the measuring tube,determined during operation on the basis of the exciter current, and/orfrom a viscosity-density product of the medium guided in the measuringtube, determined during operation on the basis of the exciter current.

In a fourth development of the method of the invention, the methodfurther includes the step of developing a second measurement valuerepresenting a density of the medium on the basis of the oscillationmeasurement signals, as well as the step of developing a correctionvalue on the basis of the second measurement value.

In a fifth development of the method of the invention, the method isused for calibrating a Coriolis mass flow measuring device and/or avibratory transducer having at least one measuring tube.

The invention rests particularly on the recognition that the exciterpower fed into the transducer for maintaining the lateral oscillationsof the measuring tube can be influenced to a great degree byinhomogeneities in the medium to be measured, homogeneities such as e.g.entrained gas bubbles, entrained solid particles, and the like. If thisexciter power, dependent on an apparent viscosity and/or aviscosity-density product of the medium guided in the measuring tube, iscompared with an actual, or at least significantly more accuratelymeasured, viscosity of the medium, obtained, for example, by acorresponding external and/or internal reference-measurement, the partinstantaneously relevant for the mass flow measurement attributable toinhomogeneities in the medium can be estimated with sufficient accuracy.A special advantage of the invention is that even the referencemeasurement of the viscosity can be performed by means of the sameCoriolis mass flow measuring device and, consequently, independently ofpossible external measurement locations.

A further advantage of the invention is that, in the case of theCoriolis mass flow measuring device of the invention, as compared to aconventional device, there is need for small changes only in the usuallydigital measurement production, essentially limited to the firmware,while, both in the case of the transducer and also in the case of theproduction and pre-processing of the oscillation measurement signals,no, or only very slight, changes are required. Thus, for example, theoscillation measurement signals can be sampled, as before, with a usualsampling ratio of far below 100:1, especially about 10:1.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and further advantageous developments thereof will now beexplained in greater detail on the basis of examples of embodimentspresented in the figures of the drawing. Equal parts are given the samereference characters in all figures; when required for clarity, alreadymentioned reference characters are omitted in subsequent drawings.

FIG. 1 shows a Coriolis mass flow measuring device which can be insertedin a pipeline for measuring a mass flow rate of a fluid flowing in thepipeline,

FIG. 2 shows, in perspective side view, an embodiment of a vibratorytransducer suited for the measuring device of FIG. 1,

FIG. 3 shows the transducer of FIG. 2 in a side view,

FIG. 4 shows the transducer of FIG. 2 in a first cross section,

FIG. 5 shows the transducer of FIG. 2 in a second section,

FIG. 6 shows a longitudinally sectioned, side view of a furtherembodiment of a vibratory transducer suited for the Coriolis mass flowmeasuring device of FIG. 1,

FIG. 7 shows schematically in the form of a block diagram a preferreddevelopment of a measuring device electronics for the Coriolis mass flowmeasuring device of FIG. 1, and

FIGS. 8, 9 are graphs of measurement data experimentally determined witha Coriolis mass flow measuring device according to the FIGS. 1 to 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

While the invention is susceptible to various modifications andalternative forms, exemplary embodiments thereof have been shown by wayof example in the drawings and will herein be described in detail. Itshould be understood, however, that there is no intent to limit theinvention to the the particular forms diclosed, but on the contrary, theintention is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by theintended claims.

FIG. 1 is a perspective illustration of a Coriolis mass flow measuringdevice 1 for registering a mass flow rate m of a medium flowing in apipeline (not shown) and for reflecting such in the form of a mass flowrate measurement value X_(m) instantaneously representing this mass flowrate. The medium can be practically any flowable material, for example aliquid, a gas, a vapor, or the like. Moreover, the Coriolis mass flowmeasurement device 1 can, on occasion, also be used for measuring adensity ρ and/or a viscosity η of the medium.

The Coriolis mass flow measuring device 1 includes for these goals avibratory measuring transducer 10, through which the medium to bemeasured flows during operation, and a measuring device electronics 50electrically connected with the transducer 10. Examples of embodimentsand developments of the transducer are shown in FIGS. 2 to 6, whileFIGS. 2 and 7 are schematic illustrations of examples of the measuringdevice electronics. Preferably, the measuring device electronics 50 isadditionally so designed that it can exchange measurement and/or otheroperational data with a measurement value processing unit superordinatedthereto, for example a programmable logic controller (PLC), a personalcomputer and/or a work station, via a data transmission system, forexample a field-bus system. Additionally, the measuring deviceelectronics 50 is so designed that it can be fed from an external powersupply, for example also over the above-mentioned field-bus system. Forthe case in which the vibration-type measuring device is to be coupledto a field bus or some other communication system, the measuring deviceelectronics 50, especially a programmable one, has a correspondingcommunications interface, e.g. for the sending of the measurement datato the already mentioned programmable logic controller or to asuperordinated process control system. For accommodating the measuringdevice electronics 50, an electronics housing 200 is additionallyprovided, either directly mounted, especially externally, on thetransducer 10, or else removed from such to some other location.

As already mentioned, the measuring device includes a vibratorymeasuring transducer 10, through which the medium to be measured flowsduring operation and which serves for producing in a medium flowingtherethrough such mechanical reaction forces, especially Coriolis forcesdependent on the mass flow rate, inertial forces dependent on mediumdensity and/or frictional forces dependent on medium viscosity, forceswhich react measurably on the transducer, especially those capable ofbeing registered by a sensor. On the basis of these reaction forcescharacterizing the medium, e.g. the flow rate, the density and/or theviscosity of the medium can be measured, in ways known to those skilledin the art.

FIGS. 3 and 4 show schematically a mechanical-electrical converterarrangement serving as an illustrative embodiment of a vibratorytransducer 10. The mechanical construction and the functioning of such aconverter arrangement is know per se to those skilled in the art anddescribed in detail e.g. also in U.S. Pat. No. 6,691,583, and in WO-A03/095949 or WO-A 03/095950.

For guiding the medium and for producing said reaction forces, thetransducer includes at least one, essentially straight measuring tube 10of predeterminable diameter, which, during operation, is caused, atleast at times, to vibrate with one or more frequencies, therebyundergoing repeated elastic deformations. Elastic deformation of themeasuring tube lumen means here that a spatial shape and/or a spatialposition of the tube lumen is cyclically, especially periodically,changed in predeterminable manner within the elastic range of themeasuring tube 10. See, in this connection, also the U.S. Pat. Nos.4,801,897, 5,648,616, 5,796,011, 6,066,609 and 6,691,583, the WO-A03/095949 and/or the WO-A 03/095950. It should be noted here that,although the transducer includes in this embodiment only a signal,straight measuring tube, a large number of other Coriolis mass flowtransducers described in the state of the art can be used instead of theillustrated transducer. In particular, for example, vibratorytransducers having two, parallel, straight measuring tubes traversed bythe medium to be measured are suitable, such as are described in detail,for example, also in the U.S. Pat. No. 5,602,345.

Measuring tube 10, which communicates in the usual manner with thepipeline supplying, respectively receiving, the medium to be measured,is mounted for oscillation in a rigid, especially bending- andtwisting-resistant, support frame 14. Instead of the tube-shaped supportframe 14 extending coaxially with the measuring tube, as shown here, ofcourse, other suitable support means, such as e.g. tubes extendingparallel to the measuring tube, or box-shaped structures, can be used.For causing the medium to flow through, the measuring tube 10 isconnected to the pipeline by way of an inlet tube piece 11 opening intoan inlet end 11# and by way of an outlet tube piece 12 opening into anoutlet end 12#. Measuring tube 10, and the inlet- and outlet-tube pieces11, 12, are, as much as possible, aligned with one another and with animaginary measuring tube longitudinal axis L and are preferably providedas one piece, so that, for their production, e.g. a single, tube-shapedworkpiece can be used; if necessary, measuring tube 10 and the tubepieces 11, 12 can, however, also be manufactured by means of separate,later-joined, e.g. welded together, workpieces. For manufacture of themeasuring tube 10, as well as also the inlet and outlet tube pieces 11,12, practically any material commonly used for such transducers can beused, such as e.g. iron-, titanium-, zirconium- and/or tantalum-alloys,synthetic materials, or ceramics. For the case where the transducer isto be releasably assembled with the pipeline, the inlet tube piece 11and the outlet tube piece 12 are each provided with respective first andsecond flanges 13, 14; if necessary, however, the inlet and outlet tubepieces 11, 12 can also be directly connected with the pipeline, e.g. bymeans of welding or brazing. Additionally, as schematically illustratedin FIG. 1, a transducer housing 100 is provided, fixed to the inlet andoutlet tube pieces 11, 12 and enclosing the measuring tube 10; compareFIGS. 1 and 2 in this connection.

For measuring the mass flow rate, the measuring tube 10 is excited tooscillate in a first oscillation mode, the so-called useful mode, inwhich it, at least in part, executes oscillations, especially bendingoscillations, laterally to the longitudinal axis L of the measuringtube, especially such that it bends laterally outwards, essentiallyoscillating at a natural bending eigenfrequency, according to a natural,first form of eigenoscillation, i.e. natural oscillation. Naturaleigenfrequencies of such lateral oscillation modes of measuring tubesare, as is known, also dependent, to a special degree, on the density ρof the medium.

For the case in which the medium in the connected pipeline is flowingand, consequently, the mass flow rate m is different from zero, Coriolisforces are induced in the flowing medium by means of the measuring tube10 oscillating in the useful mode. These forces, in turn, have an effecton the measuring tube 10, such that, in manner known to those skilled inthe art, an additional deformation of the measuring tube 10 iscoplanarly superimposed on the first form of eigenoscillation. Thisdeformation, which is essentially on the basis of a natural, second formof eigenoscillation, can be registered by sensors. The instantaneousdeflection of the deformation of the measuring tube 10 is, it sohappens, especially as concerns its amplitude, also dependent on theinstantaneous mass flow rate m. The second form of eigenoscillation, theso-called Coriolis mode, can be e.g., as usual in the case of suchtransducers, anti-symmetric forms of bending oscillations with twooscillation anti-nodes, or with four oscillation anti-nodes.

In one development of the invention, the measuring tube 10 is excitedfor producing mass flow dependent Coriolis forces in the flowing mediumat least at times with a lateral oscillation frequency f_(excL), whichcorresponds as exactly as possible to a lowest natural bendingeigenfrequency of the measuring tube 10, so that thus the laterallyoscillating measuring tube 10, when not yet containing flowing medium,is bent outwards essentially symmetrically with reference to a centralaxis perpendicular to the longitudinal axis L of the measuring tube and,in this case, shows a single oscillating anti-node. This lowest bendingeigenfrequency can, for example, lie at about 850 Hz to 900 Hz in thecase of a measuring tube 10 of stainless steel with a nominal breadth of20 mm, a wall thickness of about 1.2 mm and a length of about 350 mm,plus the usual appendages.

In another development of the invention, the measuring tube 10 isexcited for producing viscosity-dependent shear forces in the flowingmedium, at least at times, especially simultaneously with the lateraloscillations of the useful mode, with a torsional oscillation frequencyfexcT, which correspond as exactly as possible to a natural torsionaleigenfrequency of the measuring tube 10, such that it is forced to twistessentially according to a natural form of torsional oscillation aboutits longitudinal axis; see, in this connection, e.g. also the U.S. Pat.Nos. 4,524,610, 5,253,533, 6,006,609, or the EP-A 1 158 289. A lowesttorsional eigenfrequency can, for example, lie, in the case of astraight measuring tube, about in the range of twice the lowest bendingeigenfrequency.

As already indicated, the oscillations of the measuring tube 10 are, onthe one hand, damped by a sensor-registered energy loss to the medium,especially for the purpose of viscosity measurement. On the other hand,however, oscillatory energy can also be extracted from the vibratingmeasuring tube, in that components mechanically coupled thereto, such ase.g. the transducer housing 100 or the attached pipeline, are likewiseexcited to oscillate. While the, although undesired, energy loss to thetransducer housing 100 might, in fact, be calibratable, at least theenergy loss into the surroundings of the transducer, particularly to thepipeline, occurs in a manner which is not reproducible, for practicalpurposes, and may even be unpredictable. For the purpose of suppressingor preventing a possible loss of oscillation energy to the surroundings,a counter-oscillator 20 is therefore additionally provided in thetransducer, fixed at the inlet and outlet ends of the measuring tube 10.The counter-oscillator is, as schematically shown in FIG. 2, preferablybuilt in one piece. If necessary, the counter-oscillator 20 can also, asshown in U.S. Pat. No. 5,969,265, EP-A 317 340 or WO-A 00 14 485, becomposed of multiple parts or realized by means of two, separate,counter-oscillator segments fixed at the inlet and outlet ends of themeasuring tube 10; see FIG. 6. The counter-oscillator 20 serves, amongother things, to dynamically balance the transducer for a density valueof the medium expected to occur most frequently in the operation of thetransducer, or even a critical medium density value, to the extent thattransverse forces and/or bending moments possibly arising in thevibrating measuring tube 10 are, for the most part, compensated; see, inthis connection, U.S. Pat. No. 6,691,583. Beyond this, thecounter-oscillator 20 serves in the above-described case, where themeasuring tube is also excited to torsional oscillations, additionallyto produce counter-torsional moments largely compensating such torsionalmoments produced by the single measuring tube 10 twisting preferablyabout its longitudinal axis L, thus keeping the surroundings of thetransducer, especially the attached pipeline, largely free of dynamictorsional moments. The counter-oscillator 20 can, as schematically showin FIGS. 2 and 3, be provided in tube shape and, for example, be soconnected at the inlet end 11# and the outlet end 12# of the measuringtube 10, that it is, as shown in FIG. 3, essentially coaxial with themeasuring tube 10. Material for the counter-oscillator 20 can, forpractical purposes, be those usable for the measuring tube 10, thus, forexample, stainless steel, titanium alloys, etc.

In addition, the transducer 1 has, surrounding the measuring tube 10 andcounter-oscillator 20, a transducer housing 100, which protects thesecomponents from damaging environmental influences and/or damps possibleemissions of sound from the transducer to the surroundings. Thetransducer housing 100 is, in the embodiment shown here, fixed to aninlet end of the inlet tube piece and to an outlet end of the outlettube piece, in such a way that measuring tube and counter-oscillatorremain capable of oscillation in the transducer housing 100.Additionally, the transducer housing 100 is provided with a neck-liketransition piece, on which the electronics housing 200 housing themeasuring device electronics 50 is fixed; see FIG. 1.

The counter-oscillator 20, which, especially in comparison to themeasuring tube 10, is somewhat less torsionally and/or bending elastic,is caused likewise to oscillate during operation, and, indeed, atessentially the same frequency, but out of phase, especially withopposite phase, as compared to the measuring tube 10. In keeping withthis, the counter-oscillator 20 is tuned to have at least one of itstorsional eigenfrequencies as accurately as possible equal to one ofthose torsional frequencies at which the measuring tube 10 is causedmostly to oscillate during operation. Beyond this, thecounter-oscillator 20 is adjusted as accurately as possible in at leastone of its bending eigenfrequencies to equal at least one bendingoscillation frequency with which the measuring tube 10, especially inthe useful mode, is caused to oscillate and the counter-oscillator 20 isexcited during operation of the measuring transducer also to lateraloscillations, especially bending oscillations, which are developedessentially coplanarly with respect to lateral oscillations of themeasuring tube 10, especially the bending oscillations of the usefulmode.

In a development of the invention, as schematically shown in FIG. 3,grooves 201, 202 are provided, worked into the counter-oscillator, forenabling, in simple manner, an exact adjustment of its torsionaleigenfrequencies, especially a lowering of the torsionaleigenfrequencies by lowering a torsional stiffness of thecounter-oscillator 20. Although the grooves 201, 202 are shown in FIGS.2 and 3 as being essentially uniformly distributed in the direction ofthe longitudinal axis L, they can, if necessary, of course be arrangedalso non-uniformly distributed in the direction of the longitudinal axisL. Beyond this, the mass distribution of the counter-oscillator can, aslikewise shown schematically in FIG. 3, also be corrected by means ofcorresponding mass balancing bodies 101, 102, which are fixed on themeasuring tube 10. The mass balancing bodies 101, 102 can e.g. be metalrings pushed onto the measuring tube 10, or metal platelets fixed tosuch.

For producing mechanical oscillations of the measuring tube 10, thetransducer includes, additionally, an exciter arrangement 40, especiallyan electrodynamic exciter arrangement, coupled to the measuring tube.The exciter arrangement 40 serves for converting an electrical exciterpower P_(exc) fed from the measuring electronics, e.g. with a regulatedexciter current i_(exc) and/or a regulated voltage, into an excitermoment M_(exc) acting e.g. in the form of a pulse, or harmonically, on,and elastically deforming, the measuring tube 10 and/or into an exciterforce F_(exc) acting laterally on the measuring tube 10. For achieving ahighest possible efficiency and a highest possible signal/noise ratio,the exciter power P_(exc) is set as accurately as possible such thatprincipally the oscillations of the measuring tube 10 in the useful modeare maintained, and, indeed, as accurately as possible at aninstantaneous eigenfrequency of the measuring tube containing theflowing medium. The exciter force F_(exc), and also the exciter momentM_(exc), can, in this case, as, in fact, shown schematically in FIGS. 4and 6, each be in bi-directional form, or, however, also inuni-directional form, and are, in manner known to those skilled in theart, tuned as regards their amplitude e.g. by means of a current and/orvoltage regulating circuit and as regards their frequency e.g. by meansof a phase-locked loop.

The exciter arrangement 40 can, as usual for such vibratory transducers,be, for example, a plunger coil arrangement having attached to thecounter-oscillator 20, or to the inside of the transducer housing 100, acylindrical exciter coil, which conducts an appropriate exciter currenti_(exc) during operation, and having inserted at least partially in theexciter coil a permanently magnetic armature fixed to the measuring tube10. Furthermore, the exciter arrangement 40 can also be realized bymeans of multiple plunger coils, as shown e.g. in the U.S. Pat. No.4,524,610 or in WO-A 03/09950, or also by means of electromagnets.

For detecting the oscillations of the measuring tube 10, the transduceradditionally includes a sensing arrangement 60, which produces by meansof at least one, first oscillation sensor 17 reacting to vibrations ofthe measuring tube 10 an oscillation measurement signal s₁, especiallyan analog signal, representing the vibrations. The oscillation sensor 17can e.g. be formed by means of a permanently magnetic armature, which isfixed to the measuring tube 10 and which interacts with a sensor coilmounted on the counter-oscillator 20 or on the transducer housing.Especially suited as oscillation sensor 17 are those sensors that arebased on the electrodynamic principle and register a velocity of thedeflections of the measuring tube 10. Acceleration-measuring,electrodynamic, or even travel-measuring, resistive or optical, sensorscan, however, also be used. Of course, also other sensors known to thoseskilled in the art and suited for the detection of such vibrations canbe used. The sensing arrangement 60 includes, additionally, a secondoscillation sensor 18, especially one identical to the first oscillationsensor 17, by means of which it delivers a second oscillationmeasurement signal s₂ likewise representing vibrations of the measuringtube 10. The two oscillation sensors in this embodiment are arrangedseparated from one another along the length of the measuring tube 10,especially at equal distances from the middle of the measuring tube 10,such that the sensing arrangement 60 locally registers both the inlet-and the outlet-end vibrations of the measuring tube 10 and transducesthem into the corresponding oscillation measurement signals s₁ and s₂.Both oscillation measurement signals s₁, s₂, which usually each exhibita signal frequency corresponding to an instantaneous oscillationfrequency of the measuring tube 10, are, as shown in FIG. 7, fed to themeasuring device electronics 50, where they are, in manner known tothose skilled in the art, pre-processed, especially digitized, andsubsequently suitably evaluated.

In an embodiment of the invention, the exciter arrangement 40 is, asalso shown in FIGS. 2 and 3, so constructed and arranged in thetransducer that it acts in operation simultaneously, especiallydifferentially, on the measuring tube 10 and on the counter-oscillator20. In the case of this further development of the invention, theexciter arrangement 40 is, as also shown in FIG. 2, advantageously soconstructed and so arranged in the transducer, that it acts in operationsimultaneously, especially differentially, on the measuring tube 10 andon the counter-oscillator 20. In the embodiment shown in FIG. 4, theexciter arrangement 40 has a first exciter coil 41 a, which, inoperation, contains, at least at times, the exciter current, or anexciter current component. The exciter coil 41 a is fixed to a lever 41c connected to the measuring tube 10 and, by way of the lever and anarmature 41 b fixed from the outside to the counter-oscillator 20, actsdifferentially on the measuring tube 10 and the counter-oscillator 20.The arrangement has, among other things, also the advantage that, on theone hand, the counter-oscillator 20, and, consequently, also thetransducer housing 100, are kept small, and, in spite of this, excitercoil 41 a is easily accessible, especially also during assembly. Inaddition to this, another advantage of this embodiment of the exciterarrangement 40 is that possibly used coil cups 41 d, whose weightespecially at nominal widths above 80 mm is no longer negligible, can befixed likewise on the counter-oscillator 20 and, consequently, havepractically no influence on the eigenfrequencies of the measuring tube10. It is, however, to be noted here that, if needed, the exciter coils41 a can also be held by the counter-oscillator 20, and, then thearmature 41 b is held by the measuring tube 10.

In corresponding manner, the oscillation sensors 17, 18 can also be sodesigned and arranged in the transducer that vibrations of the measuringtube 10 and counter-oscillator 20 are differentially registered by them.In the embodiment shown in FIG. 5, the sensor arrangement 50 includes asensor coil 51 a fixed on the measuring tube 10, here located outside ofall principle axes of inertia of the sensor arrangement 50. The sensorcoil 51 a is located as near as possible to an armature 51 b fixed onthe counter-oscillator 20 and so magnetically coupled with this armature51 b that a measurement voltage is induced in the sensor coil and variesas a function of rotational and/or lateral, relative movements betweenmeasuring tube 10 and counter-oscillator 20, when they change theirrelative position and/or relative separation. On the basis of such anarrangement of the sensor coil 51 a, both the above-mentioned torsionaloscillations and also the excited bending oscillations can beadvantageously simultaneously registered. If required, the sensor coil51 a can, however, also be fixed for this purpose on thecounter-oscillator 20, and, in corresponding manner, the armature 51 bcoupled therewith fixed on the measuring tube 10.

In another embodiment of the invention, measuring tube 10,counter-oscillator 20, and the sensor- and exciter-arrangements 40, 50affixed thereto, are so matched to one another with respect to theirmass distributions, that the so-formed internal part of the transducer,suspended by means of the inlet and outlet tube pieces, exhibits acenter of mass MS, which lies at least inside of the measuring tube 10,preferably, however, as near as possible to the measuring tubelongitudinal axis L. Furthermore, the internal part is advantageously soconstructed, that it exhibits a first principle axis of inertia T₁aligned with the inlet tube piece 11 and the outlet tube piece 12 and atleast sectionally lying inside of the measuring tube 10. Because of thedisplacement of the center of mass MS of the internal part, especially,however, also because of the above-described position of the firstprinciple axis of inertia T₁, the two oscillation forms assumed duringoperation by the measuring 10 and substantially compensated by thecounter-oscillator 20, namely the torsional oscillations and the bendingoscillations of the measuring tube 10, are mechanically decoupled fromone another to the greatest extent possible; see, in this connection,also the WO-A 03/095950. In this way, both oscillation forms, thuslateral oscillations and/or torsional oscillations, can, without more,be advantageously excited separately from one another. Both thedisplacement of the center of mass MS and also the first principle axisof inertia T₁ towards the longitudinal axis L of the measuring tube can,for example, be considerably simplified, when the internal part, thusmeasuring tube 10, counter-oscillator 20, and the sensor- andexciter-arrangements 50, 40 affixed thereto, are so constructed andarranged with respect to one another that a mass distribution of theinternal part along the longitudinal axis L of the measuring tube isessentially symmetrical, at least, however, invariant, with respect toan imagined rotation about the longitudinal axis L of the measuring tubeby 180° (c2-symmetry). In addition, the, here, tube-shaped, especiallyalso predominantly axial-symmetric, counter-oscillator 20 is arrangedessentially coaxially with the measuring tube 10, so that theachievement of a symmetrical mass distribution of the internal part isconsiderably simplified and, consequently, the center of mass MS isshifted in simple manner near to the longitudinal axis of the measuringtube. Moreover, the sensor- and exciter-arrangements 50, 40 in theembodiment are so constructed and arranged with respect to one anotheron the measuring tube 10 and perhaps also on the counter-oscillator 20,that a mass moment of inertia is formed as concentrically as possiblewith the longitudinal axis L of the measuring tube, or, at least, keptas small as possible. This can e.g. be achieved such that a commoncenter of mass of sensor- and exciter-arrangements 50, 40 lies likewiseas near as possible to the longitudinal axis L of the measuring tubeand/or that a total mass of sensor- and exciter arrangements 50, 40 iskept as small as possible.

In a further development of the invention, the exciter arrangement 40,for the purpose of separated excitement of torsional- and/orbending-oscillations of the measuring tube 10, is so constructed and sofixed to tube 10 and to the counter-oscillator, that a force producingthe bending oscillations acts on the measuring tube along an imaginaryforce line extending outside of a second principle axis of inertia T₂perpendicular to the first principle axis of inertia T₁ or cutting theformer in at most one point. Preferably, the inner part is so developed,that the second principle axis of inertia T₂ essentially coincides withthe above-mentioned central axis. In the embodiment shown in FIG. 4, theexciter arrangement 40 has for this purpose at least one exciter coil 41a, which contains in operation, at least at times, the exciter currentor an exciter current component and which is fixed to a lever 41 cconnected to the measuring tube 10 and, by way of the lever and anarmature fixed from the outside to the counter-oscillator 20, actsdifferentially on the measuring tube 10 and the counter-oscillator 20.The arrangement has, among other things, also the advantage that, on theone hand, the counter-oscillator 20, and, consequently, also thetransducer housing 100, are kept small, and, in spite of this, excitercoil 41 a is easily accessible, especially also during assembly. Inaddition to this, another advantage of this embodiment of the exciterarrangement 40 is that possibly used coil cups 41 d, whose weightespecially at nominal widths above 80 mm is no longer negligible, can befixed likewise on the counter-oscillator 20 and, consequently, havepractically no influence on the eigenfrequencies of the measuring tube10. It is, however, to be noted here that, if needed, the exciter coils41 a can also be held by the counter-oscillator 20, and, then thearmature 41 b is held by the measuring tube 10.

In a further development of the invention, the exciter arrangement 40has at least one, second exciter coil 42 a arranged along a diameter ofthe measuring tube 10 and coupled with the measuring tub 10 and thecounter-oscillator 20 in the same way as the exciter coil 41 a. Inanother preferred development of the invention, the exciter arrangementhas two further exciter coils 43 a, 44 a, thus at least four, arrangedsymmetrically with reference to the second principle axis of inertia T₂and all mounted in the transducer in the previously described manner.The force acting on the measuring tube 10 outside of the secondprinciple axis of inertia T₂ can be produced by means of such two- orfour-coil arrangements in simple manner, e.g. by providing one of theexciter coils, e.g. the exciter coil 41 a, with a different inductanceas compared with, in each case, the other, or by having one of theexciter coils, e.g. the exciter coil 41 a, contain in operation anexciter current component that is different from, in each case, anexciter current component of, in each case, the other exciter coils.

In another development of the invention, the sensor arrangement 50includes, as shown schematically in FIG. 5, a sensor coil 51 a fixed onthe measuring tube 10 and arranged outside of the second principle axisof inertia T₂. The sensor coil 51 a is located as near as possible to anarmature 51 b fixed on the counter-oscillator 20 and so magneticallycoupled with this armature 51 b that a measurement voltage is induced inthe sensor coil and varies according to rotational and/or lateral,relative movements between measuring tube 10 and counter-oscillator 20as they change their relative position and/or relative separation. Onthe basis of such an arrangement of the sensor coil 51 a, both theabove-mentioned torsional oscillations and also the excited bendingoscillations can be advantageously simultaneously registered. Ifrequired, the sensor coil 51 a can, however, also be fixed for thispurpose on the counter-oscillator 20, and, in corresponding manner, thearmature 51 b coupled therewith fixed on the measuring tube 10.

It is noted here, further, that the exciter arrangement 40 and thesensor arrangement 50 can be constructed to have essentially equalmechanical structures in the manner known to those skilled in the art;consequently, the above-described embodiments of the mechanicalstructure of the exciter arrangement 40 can essentially be transferredto the mechanical structure of the sensor arrangement 50, and viceversa.

For causing the measuring tube 10 to vibrate, the exciter arrangement 40is, as already mentioned, fed by means of a likewise oscillating excitercurrent i_(exc), especially one oscillating at more than one frequency,of adjustable amplitude and adjustable exciter frequency f_(exc), insuch a manner that the exciter coils 26, 36 are traversed by such duringoperation and the magnetic fields required for moving the armatures 27,37 are correspondingly produced. The exciter current i_(exc) can e.g. beharmonic, multi-frequency or even rectangular. The lateral oscillationexciter frequency f_(excL) of a lateral current-component i_(excL) ofthe exciter current needed to maintain the lateral oscillations of themeasuring tube 10 can be selected and adjusted in the transducer shownin the embodiment advantageously such that the laterally oscillatingmeasuring tube 10 oscillates preferably in a bending oscillation,fundamental mode with a single oscillation antinode. Analogouslythereto, also a torsional oscillation exciter frequency f_(excT) of atorsional current-component i_(excT) of the exciter current i_(exc)needed to maintain the torsional oscillations of the measuring tube 10can be selected and adjusted in the transducer shown in the embodimentadvantageously such that the torsionally oscillating measuring tube 10oscillates preferably in a torsional oscillation, fundamental mode witha single oscillation antinode.

For the above-described case, that the lateral oscillation frequencyf_(excL) and the torsional oscillation frequency f_(excT), with whichthe measuring tube is caused to oscillate during operation, are adjustedto be different from one another, a separation of the individualoscillation modes can occur both in the exciter signals and in thesensor signals in simple and advantageous manner by means of thetransducer, even in the case of simultaneously excited torsional andbending oscillations, e.g. based on a signal filtering or a frequencyanalysis.

For producing and adjusting the exciter current i_(exc), the measuringdevice electronics 50 includes a suitable driver circuit 53, which iscontrolled by a lateral oscillation frequency setting signal y_(FML)representing the lateral oscillation exciter frequency f_(excL), and bya lateral oscillation amplitude setting signal y_(AML) representing thelateral oscillation amplitude, which are to be set for the excitercurrent i_(exc) and/or the lateral current-component i_(excL), as wellas, at least at times, by a torsional oscillation frequency settingsignal y_(FMT) representing the torsional oscillation exciter frequencyf_(excT), and by a torsional oscillation amplitude setting signaly_(AMT) representing the torsional oscillation amplitude, which are tobe set for the exciter current i_(exc) and/or the torsionalcurrent-component i_(excT). The driver circuit can be embodied e.g. bymeans of a voltage-controlled oscillator and a voltage-to-currentconverter connected downstream; instead of an analog oscillator,however, e.g. also a numerically controlled, digital oscillator can beused for adjusting the instantaneous exciter current i_(exc), or thecomponents i_(excL), i_(excT), of the exciter current.

For producing the lateral oscillation amplitude setting signal y_(AML)and/or the torsional oscillation amplitude setting signal y_(AMT), e.g.an amplitude regulation circuit 51 can be integrated into the measuringdevice electronics 50. Circuit 51 updates the amplitude adjustingsignals y_(AML), y_(AMT) on the basis of instantaneous amplitudes of atleast one of the two oscillation measurement signals s₁, s₂, measured atthe instantaneous lateral oscillation frequency and/or the instantaneoustorsional oscillation frequency, as well as on the basis of suitable,constant or variable amplitude reference values for the lateral,respectively the torsional, oscillations W_(B), W_(T); if necessary,also instantaneous amplitudes of the exciter current i_(exc) can beintroduced for generating the lateral oscillation amplitude adjustmentsignal y_(AMT) and/or the torsional oscillation amplitude adjustmentsignal y_(AMT); compare FIG. 7. Construction and functioning of suchamplitude regulating circuits are likewise known to those skilled in theart. As an example for such an amplitude regulating circuit, referenceis also made to measurement transmitters of the series “PROMASS 80”,such as are offered by the assignee, for example in connection withmeasuring transducers of the series “PROMASS I”. Its amplituderegulating circuit is preferably so designed, that the lateraloscillations of the measuring tube 10 are regulated to a constant (thusalso independent of the density ρ) amplitude.

The frequency regulating circuit 52 and the driver circuit 53 can e.g.be embodied as a phase-locked loop, which is used in the manner known tothose skilled in the art, for continuously adjusting the lateraloscillation frequency setting signal y_(FML) and/or the torsionaloscillation frequency setting signal y_(FMT) to the instantaneouseigenfrequencies of the measuring tube 10 on the basis of a phasedifference measured between at least one of the oscillation measurementsignals s₁, s₂ and the exciter current i_(exc) to be adjusted,respectively the exciter current i_(exc) as instantaneously measured.The construction and use of such phase-locked loops for drivingmeasuring tubes at their mechanical eigenfrequencies is e.g. describedin detail in U.S. Pat. No. 4,801,897. Of course, also other frequencyregulation circuits known to those skilled in the art can be used, suchas e.g. that of U.S. Pat. Nos. 4,524,610 or 4,801,897. Additionally,reference is made to the already mentioned measurement transmitters ofthe series “PROMASS 80” regarding an application of such frequencyregulating circuits for vibratory measuring transducers. Other circuitssuited as driver circuits can also be taken, for example, from one ofthe U.S. Pat. Nos. 5,869,770 or 6,505,519.

In another embodiment of the invention, the amplitude regulating circuit51 and the frequency regulating circuit 52 implemented, as schematicallyillustrated in FIG. 7, by means of a digital signal processor DSPprovided in the measuring device electronics 50 and by means of programcode correspondingly implemented, and running, in the DSP. The programcode can be stored persistently or even permanently e.g. in anon-volatile memory EEPROM of a microcomputer 55 controlling and/ormonitoring the signal processor and can be loaded during booting of thesignal processor DSP into a volatile data-storing RAM of the measuringdevice electronics 50 e.g. integrated in the signal processor DSP.Signal processors for such applications are available commercially, e.g.those of type TMS320VC33 of Texas Instruments. It is, of course,practically self-evident that the oscillation measurement signals s₁, s₂are to be converted into corresponding digital signals by means ofcorresponding analog-to-digital converters A/D for processing in thesignal processor DSP; see EP-A 866,319 in this connection. Should it benecessary, the adjusting signals issued by the signal processor, such ase.g. the amplitude adjusting signals y_(AML), y_(AMT), or the frequencyadjusting signals y_(FML), y_(FMT), can be converted in correspondingmanner from digital to analog.

As illustrated in FIG. 7, the oscillation measurement signals s₁, s₂ areadditionally fed to a measuring circuit 21 of the measuring deviceelectronics. The measuring circuit 21, which is at least partiallyconstructed to function as a flow rate computer, serves, in manner knownper se to those skilled in the art, for determining, on the basis of aphase difference detected between the two, if necessary suitablypre-conditioned, oscillation measurement signals s₁, s₂, a mass flowrate measurement value X_(m) corresponding to the mass flow rate to bemeasured. Suitable to serve as the measuring circuit 21 areconventional, especially digital, measuring circuits, which determinemass flow rate on the basis of oscillation measurement signals s₁, s₂;see, in this connection, the initially mentioned WO-A 02/37063, WO-A99/39164, or the U.S. Pat. Nos. 5,648,616 and 5,069,074. Of course, alsousable are other measuring circuits known to those skilled in the art tobe suitable for Coriolis mass flow rate measuring devices for measuringand appropriately evaluating the phase- and/or time-differences betweenoscillation measurement signals of the described kind. Measurementcircuit 21 also serves for producing a density measurement value X_(ρ)representing an instantaneous density ρ of the medium or a phase of themedium.

As already mentioned at the start, inhomogeneities and/or the formationof first and second phases in the flowing medium, for example gasbubbles and/or solids particles entrained in liquids, can mean that themeasurement value determined in the usual way assuming a single phaseand/or homogeneous medium may not agree sufficiently accurately with theactual mass flow rate, i.e. it must be accordingly corrected. Thisinitially determined measurement value, which provisionally representsthe mass flow rate or at least corresponds therewith, and which, in thesimplest case, can be a phase difference measured between theoscillation measurement signals s₁, s₂, is, therefore, referred to inthe following as a first intermediate value X′_(m). The mass flow ratemeasurement value X_(m) representing the mass flow rate sufficientlyaccurately is finally derived by the evaluation electronics 21 from thisfirst intermediate value X′_(m). There is already discussion in thestate of the art concerning this, that such inhomogeneities in themedium immediately affect, besides the phase difference measured betweenthe two oscillation measurement signals s₁, s₂, also the oscillationamplitude and the oscillation frequency of each of the two oscillationmeasurement signals, respectively the exciter current, and,consequently, practically every operational parameter usually measured,directly or indirectly, in the use of measuring devices of the describedtype. This is true, in fact, especially, as also explained in WO-A03/076880 or U.S. Pat. No. 6,505,519, for the operational parametersdetermined in the case of laterally oscillating measuring tubes; it can,however, also not always be excluded for those operational parameterswhich are measured with torsionally oscillating measuring tubes; see, inthis connection, especially U.S. Pat. No. 4,524,610.

Advanced investigations on the part of the inventors have led, however,to the surprising discovery that, while the instantaneous excitercurrent i_(exc) and, concomitantly, a damping of the oscillations of themeasuring tube usually also measured during operation of the measuringdevice and/or a viscosity of the medium measured during operation,depend to a considerable degree on the amount of the inhomogeneity ofthe two- or more-phase medium and/or on a concentration of a secondphase of the same, and, for example, thus from an eruption, adistribution and/or an amount of the gas bubbles and/or solids particlesentrained in a liquid to be measured, nevertheless both for lateral andfor torsional oscillations—at least in the above-mentioned fundamentalmodes—a largely reproducible and, consequently, at least experimentallydeterminable relationship can be postulated between the instantaneousexciter current i_(exc) or an, in each case, effective componenti_(excL), i_(excT) of the same and the degree of the inhomogeneity ofthe two or more-phase medium or the concentration of a second phase,especially a second phase acting as an interference. Additionally, ithas been discovered, surprisingly, that a correction of the intermediatevalue X′_(m) can be performed, taking into consideration the actualviscosity of the medium to be measured, respectively the phase of themedium mainly to be measured, and taking the exciter current i_(exc)into consideration, which, it is recognized, can serve as a measure ofan apparent viscosity or also a viscosity-density product of the mediumguided in the measuring tube 11, or on the basis of at least a componenti_(excL), i_(excT) of the exciter current required for maintaining theinstantaneous oscillations of the measuring tube.

For the exact measurement of mass flow rate, even in the case of two- ormore-phase medium, a second, especially digital, intermediate value X₂is formed during operation by means of the measuring device electronics2 on the basis of the exciter current i_(exc), especially the regulatedexciter current, and/or a component i_(excL), i_(excT) thereof. Thesecond intermediate value X₂ corresponds to a damping of theoscillations of the measuring tube 11. This damping is a function of anapparent viscosity and/or a viscosity-density product of the mediumguided in the measuring tube 11. Additionally, a correction value X_(K),especially likewise a digital value, is determined for the intermediatevalue X′_(m) by the measuring circuit 21 by using the secondintermediate value X₂ and taking into consideration an initiallysuitably determined viscosity measurement value X_(η), which correspondsto the actual viscosity of the medium guided in the measuring tube 11 orat least to a reference viscosity predetermined for the medium. Thecorrection of the intermediate value X′_(m) on the basis of thecorrection value X_(K) and the generating of the mass flow ratemeasurement value X_(m) can occur in the measuring device electronicsfor example based on the mathematical relationshipX _(m) =K _(m)·(1+X _(K))·X′ _(m)  (1)

In an embodiment of the invention, the correction value X_(K) isdetermined by means of the measuring device electronics based on themathematical relationshipX _(K) =K _(K)·(X ₂ −X _(η))  (2)so that this is practically a measure for a deviation Δη of theviscosity η of the medium from an apparent viscosity η* of the mediumguided in the measuring tube, as determined during operation on thebasis of the exciter current i_(exc) and/or a component of the excitercurrent i_(exc), and/or from a viscosity-density product ηρ of themedium guided in the measuring tube, as determined during operation onthe basis of the exciter current i_(exc). Alternatively, or as asupplement thereto, the correction value X_(K) can be determined,furthermore, on the basis of the mathematical relationship

$\begin{matrix}{X_{K} = {K_{K}^{\prime} \cdot \left( {1 - \frac{X_{\eta}}{X_{2}}} \right)}} & (3)\end{matrix}$

Thus, while, in Equation (2), the correction value X_(K) is determinedon the basis of a difference Δη existing between the intermediate valueX₂ and the viscosity measurement value X_(η), which corresponds, inturn, practically to an absolute error between the two measured values,Equation (3) determines the correction value X_(K) on the basis of acomparison of the second intermediate value X₂ with the viscositymeasurement value X_(η) or also on the basis of a relative error Δη/η*between the two measured values X₂, X_(η). In this respect, thecorrection value X_(K) represents, at least for a two-phase medium, alsoa measure for an instantaneous, relative or absolute concentration of afirst or a second phase of the medium, especially for gas bubbles in aliquid. Besides the generating of the mass flow rate measurement valueX_(m), the intermediate value X₂ can, consequently, also be usedadvantageously, additionally, e.g. for signaling, e.g. on site or in aremote control room, in visually observable manner, the degree ofinhomogeneity of the medium or measurements derived therefrom, such ase.g. a percent air content in the medium or a volume-, quantity-, ormass-fraction of solids particles entrained in the medium.

Additional experimental investigations have shown that, for a transduceraccording to the illustrated example of an embodiment, consideration ofthe instantaneous lateral oscillation frequency of the vibratingmeasuring tube can lead to a further improvement of the accuracy of themass flow rate measurement value X_(m). Moreover, a normalizing of thecorrection value X_(K) determined from Equation (2) or (3) with thesquare root of the instantaneous lateral oscillation frequency canachieve that the correction value X_(K) is essentially proportional tothe gas fraction, at least for the case that a liquid, for exampleglycerin, is to be measured having entrained gas bubbles, for exampleair; reference, in this connection, also FIG. 9. Thus, according to afurther development of the invention, Equation (2) is modified using alateral oscillation frequency measurement value X_(fexcL) representingthe instantaneous lateral oscillation frequency, as follows:

$\begin{matrix}{X_{K} = {K_{K} \cdot \frac{\left( {X_{2} - X_{\eta}} \right)}{\sqrt{X_{fexcL}}}}} & (4)\end{matrix}$

The determining of the lateral oscillation frequency measurement valuecan occur in simple manner, e.g. on the basis of the above-mentionedlateral oscillation frequency regulating signal y_(FML).

It is known that the damping of the oscillations of the measuring tube10 is determined not only by a damping component attributable to viscousfriction within the medium, but also by a damping component practicallyindependent of the medium. This latter component is caused by mechanicalfriction forces, which e.g. act in the exciter arrangement 40 and in thematerial of the measuring tube 10. Stated differently, theinstantaneously measured exciter current i_(exc) represents the totalityof the frictional forces and/or frictional torques in the transducer 10,including both the mechanical frictions in the transducer and theviscous friction in the medium. In the determining of the intermediatevalue X₂, which, as already mentioned, should correspond mainly with thedamping attributable to viscous frictions in the medium, themedium-independent, mechanical damping component is to be appropriatelyconsidered, especially appropriately separated out, or eliminated.

For determining the intermediate value X₂, one embodiment of theinvention thus provides that there is subtracted from a total excitercurrent measurement value X_(iexc), especially a digital such value,instantaneously representing the exciter current i_(exc), and/or from alateral current measurement value X_(iexcL), especially a digital suchvalue, instantaneously representing the lateral current componenti_(excL), and/or from a torsional current measurement value X_(iexcT),especially a digital such value, instantaneously representing thetorsional current component i_(excT), in each case a correspondinglyassociated total empty current measurement value K_(iexc), lateral emptycurrent measurement value K_(iexcL), respectively a torsional emptycurrent measurement value K_(iexcT), of which each represents themechanical friction forces arising in the transducer in the case ofempty measuring tube 10. Each of the empty current measurement valuesK_(iexc), K_(iexcL), K_(iexcT) is likewise to be determined during acalibration of the Coriolis mass flow rate measuring device, e.g. for anevacuated measuring tube 10, or one carrying only air, and appropriatelystored or installed in the measurement device electronics 50, especiallyas normalized to the oscillation amplitude associated therewith. It isclear, without further explanation, for one skilled in the art that, ifrequired, other physical parameters influencing the empty currentmeasurement values K_(iexc), K_(iexcL), K_(iexcT), parameters such ase.g. an instantaneous temperature of the measuring tube and/or medium,can be considered in their calibration. For calibrating the measuringtransducer 10, usually two or more, different, two- or more-phase mediahaving varying, but known, flow parameters, such as e.g. knownconcentrations of the individual medium phases of the calibratingmedium, its density ρ, mass flow rate m, viscosity η and/or temperature,are caused to flow serially through the measuring transducer 10 and thecorresponding reactions of the measured value transducer 10, reactionssuch as the instantaneous exciter current i_(exc), the instantaneouslateral oscillation exciter frequency f_(excL) and/or the instantaneoustorsional oscillation exciter frequency f_(excT), are measured. The setflow parameters and each measured reaction of the measured operationalparameters of the measuring transducer 10 are matched appropriately toone another and, consequently, mapped for the corresponding calibrationconstants. For example, for determining the constants in the case of thecalibration measurement for two calibration media of known viscosityheld as constant as possible and of inhomogeneity developed indifferent, but in each case unchanging, manner, a ratio X_(m)′/m and/orX_(m)/m is formed, of the, in each case, determined intermediate valueX_(m)′, respectively of the, in each case, determined mass flow ratemeasurement value X_(m), to the, in each case, current mass flow rate atknown air fraction. For example, the first calibrating medium can beflowing water, or even oil, with entrained air bubbles, and the secondcalibration medium can be water, or even oil, which is as homogeneous aspossible. The determined calibration constants can then be e.g. storedin the form of digital data in a table memory of the measuring deviceelectronics; they can, however, also serve as analog setting values forcorresponding computational circuits. It is to be noted here that thecalibration of measuring transducers of the described type is known, perse, to those skilled in the art, or at least to be comprehended on thebasis of the above explanations and, consequently, no furtherexplanation is required. Advantageously, for determining the totalexciter current measurement X_(iexc), the lateral current measurementX_(iexcL) and/or the torsional current measurement X_(iexcT), thealready mentioned lateral oscillation amplitude setting signal y_(AML)and/or the torsional oscillation amplitude setting signal y_(AMT) can beused, since these represent the exciter current i_(exc) or itscomponents i_(excL), i_(excT) sufficiently accurately for thecorrection.

In a further embodiment of the invention, the determining of thecorrection value therein occurs, as also shown in FIG. 8, by way ofexample, using experimentally determined current measurement valuesX_(iexcL), X_(iexcT) and empty current measurement values K_(iexcL),K_(iexcT), on the basis of the lateral current component i_(excL)driving the lateral oscillations and on the basis of the associatedlateral empty current measurement value K_(iexcL), especially based onthe mathematical relationshipX ₂ =K ₂·(X _(iexcL) −K _(iexcL))  (5)and/or based on the mathematical relationship

$\begin{matrix}{X_{2} = {K_{2}^{\prime} \cdot \left( {1 - \frac{K_{iexcL}}{X_{iexcL}}} \right)}} & (6)\end{matrix}$

In case necessary, especially in the case of oscillation amplitudes ofthe vibrating measuring tube significantly varying during operationand/or deviating from the calibrated reference values, the lateralcurrent component i_(excL) can initially likewise be normalized on theinstantaneous oscillation amplitude of the lateral oscillations of themeasuring tube, for example using the oscillation measurement signalss₁, s₂.

In a further embodiment of the invention, the viscosity measurementvalue X_(η) represents a predetermined reference viscosity, which isdetermined in advance. For example, used for this can be the viscositymeasurement value based on knowledge of the medium to be measured, fedin from a remote control location or manually on site, or transmittedfrom an external viscosity meter to the measuring device electronics viaa field bus.

In a further development of the invention, the viscosity measurementvalue X_(η) is produced by means of the measurement electronics 2itself.

For the above-described case, namely, that the straight measuring tubeis caused to oscillate in operation simultaneously or alternatingly,laterally and torsionally, the viscosity measurement value can, however,also be determined in operation directly by Coriolis mass flow measuringdevice 1 using measuring transducer 1 and measuring device electronics2. Straight measuring tubes can, as is known, when excited to torsionaloscillations about a torsional oscillation axis extending parallel to,or coinciding essentially with, the measuring tube longitudinal axis,effect that shear forces are produced in the medium guided therethrough,whereby, in turn, significant oscillation energy is sapped from thetorsional oscillations. As a result, a significant damping of thetorsional oscillations of the oscillating measuring tube, for themaintenance of which extra electrical exciting power P_(exc) must be fedto the measuring tube. Using the electrical exciting power P_(excT)needed for maintaining the torsional oscillations of the measuring tube10, those skilled in the art can, in known manner, make use of themeasuring transducer to determine, at least approximately, also theviscosity η of the medium; see, in this connection, especially also anyone of the U.S. Pat. Nos. 4,524,610, 5,253,533, 6,006,609 and 6,651,513.

It has been found, surprisingly, that, in spite of that fact that boththe exciter current i_(exc), or lateral current component i_(excL)needed for maintaining the lateral oscillations of the measuring tube 10and, as discussed especially in U.S. Pat. No. 4,524,610 or EP-A 1 291639, the exciter current i_(exc) or torsional current component i_(excT)needed for maintaining the torsional oscillations of the measuring tube10 are dependent to a significant degree on the degree of theinhomogeneity or on the concentrations of the individual medium phases,the inclusion of the viscosity measurement value X_(η) produced in theabove-described manner by means of the Coriolis mass flow measuringdevice 1 itself enables an amazingly robust and very well reproduciblecorrection of the intermediate value X′_(m) and, consequently, also thegenerating of a very accurate mass flow rate measurement value X_(m).

Thus, in a first variant of this further development of the invention,wherein also the viscosity measurement value X_(η) is produced by meansof the measuring device electronics 2, this is determined on the basisof the exciter current i_(exc) driving the exciter arrangement 40 in thecase of the measuring tube oscillating at least partially torsionally,especially on the basis of the torsional current component i_(excT)serving for maintaining the torsional oscillations of the measuring tube10. Moreover, also the intermediate value X₂ and/or the correction valueX_(K) are/is calculated based on this internally determined viscositymeasurement value X_(η). Taking into consideration the relationshipalready described in U.S. Pat. No. 4,524,610:√{square root over (η)}˜i_(excT),  (7)according to which the torsional current component i_(excT) reduced bythe above-mentioned torsional empty current measurement value K_(iexcT)correlates very well with the square root of the actual viscosity η, atleast in the case of constant density ρ, correspondingly for determiningthe viscosity measurement value X_(η), first, internally in themeasuring device electronics, a squared value X_(ΔiexcT) ² is formedfrom the torsional current measurement value X_(iexcT) derived from theexciter current i_(exc), reduced by the torsional empty currentmeasurement value K_(iexcT). Starting there, the viscosity measurementvalue X_(η) is numerically determined, according to a further embodimentof the invention, based on the mathematical relationship:

$\begin{matrix}{X_{\eta} = {K_{\eta} \cdot {\frac{X_{\Delta\;{iexcT}}^{2}}{X_{\rho}}.}}} & (8)\end{matrix}$where K_(η) is a device constant, especially one also dependent on thegeometry of the measuring tube 10. The density measurement value X_(ρ)appearing in the denominator of the formula merely cares for the factthat the square of the current actually provides information on theproduct of density and viscosity; see also, in this connection, U.S.Pat. No. 4,524,610.

The viscosity measurement value X_(η) determined according to thismathematical relationship provides a good approximation for a dynamicviscosity of the fluid, which, as is known, can be formed also as theproduct of kinematic viscosity and density, ρ, of the fluid. If theviscosity measurement value X_(η) is to serve as an approximation of thekinematic viscosity, then, before its output, a correspondingnormalizing must be done on the density measurement value X_(ρ), e.g. bymeans of a simple numerical division. For this purpose, Equation (8) canbe modified as follows:

$\begin{matrix}{X_{\eta} = {K_{\eta} \cdot \left( \frac{X_{\Delta\;{iexcT}}}{X_{\rho}} \right)^{2}}} & (9)\end{matrix}$

In a further embodiment of the invention, the square X_(iexcT) ² of thetorsional current measurement value X_(iexcT) is normalized for formingthe viscosity measurement value X_(η) by means of a simple numericaldivision on an amplitude measurement value X_(sT), which represents aninstantaneous, operationally possibly varying signal amplitude of atleast one of the oscillation measurement signals s₁, s₂, in the case ofa torsionally oscillating measuring tube. Thus, it has been found,additionally, that, for such viscosity measuring devices using such avibratory transducer, and especially also at constantly regulatedoscillation amplitude and/or at simultaneous excitation of lateral andtorsional oscillations, a ratio i_(exc)/θ of the exciter current i_(exc)to a practically not-directly measurable velocity of a movement causingthe internal frictions and thus also the frictional forces in the mediumis a more accurate approximation for the already mentioned dampingopposing the deflections of the measuring tube 10. Therefore, forfurther increasing the accuracy of the viscosity measurement valueX_(η), especially however also for decreasing its sensitivity tofluctuating oscillation amplitudes of the vibrating measuring tube 10possibly occurring during operation, it is further provided that, fordetermining the viscosity measurement value X_(η), the torsional currentmeasurement value X_(iexcT) is first normalized on the amplitudemeasurement value X_(sT), which represents, with sufficient accuracy,the above-mentioned velocity θ. Stated differently, a normalizedtorsional current measurement value X′_(iexcT) is formed using thefollowing formula:

$\begin{matrix}{X_{iexcT}^{\prime} = \frac{X_{iexcT}}{X_{sT}}} & (10)\end{matrix}$

The amplitude measurement value X_(s1) is preferably derived from the atleast one, possibly already digitized, sensor signal s₁ by means of themeasuring device electronics 50, e.g. by means of an internal amplitudemeasurement circuit, based on the recognition that the motion causingthe viscous friction in the medium corresponds very strongly with themovement of the vibrating measuring tube 10 registered by means of thesensor 51 or also locally registered by means of the sensor 51. Usingthe normalized torsional current measurement value X′_(iexcT), theviscosity measurement value can then be determined e.g. according to thefollowing formula:

$\begin{matrix}{X_{\eta} = {K_{\eta} \cdot \frac{X_{iexcT}^{\prime 2}}{K_{f} \cdot X_{\rho}}}} & (11)\end{matrix}$

The correction factor K_(f) introduced in this equation serves solely toweight the density measurement value X_(ρ) with the current oscillationfrequency of the vibrating measuring tube 10. It is noted here by way ofrepetition that the sensor signal s₁ is preferably proportional to avelocity of an especially lateral deflection movement of the vibratingmeasuring tube 10; the sensor signal s₂ can, however also be e.g.proportional to an acceleration acting on the vibrating measuring tubeand to a distance traveled by the vibrating measuring tube 10. For thecase where the sensor signal s₁ is designed in the above sense to bevelocity proportional, the correction factor Kf corresponds to theoscillation frequency of the vibrating measuring tube 10, while it ise.g. equal to the third power of the oscillation frequency in the caseof a distance-proportional sensor signal s₁.

Instead of measuring the excitation energy E_(exc), or even insupplementation thereof, a further possibility for determining theviscosity of the medium is to measure and appropriately evaluate apressure difference over a suitable measurement distance along thepipeline or along the measuring tube 10; see, in this connection,especially one of the U.S. Pat. Nos. 5,359,881 or 6,513,393. At least inthe case of essentially laminar flow in the measurement section, theviscosity measurement value for the correction of the intermediate valueX′_(m) can be determined with sufficient accuracy using the followingmathematical relationship:

$\begin{matrix}{X_{\eta} = {K_{p} \cdot \frac{X_{\Delta\; p}}{X_{m}^{\prime}} \cdot X_{\rho}}} & (12)\end{matrix}$

Equation (12) is based fundamentally on the known Hagen-Poiseuille law,with the calibration factor Kρ being an initially determinable parameterdepending especially on a diameter and a length of the measurementsection. For implementing this mathematical relationship, the measuringdevice electronics 2 is, in a second variant of this further developmentof the invention, in which also the viscosity measurement value X_(η) isproduced by means of the measuring device electronics 2, at least attimes coupled with a differential pressure sensor, which at least attimes delivers a pressure difference measurement value X_(Δp)representing a pressure difference measured along the pipeline and/oralong the measuring tube.

The above-presented functions serving for producing the mass flow ratemeasurement value X_(m), symbolized by the Equations (1) to (12), can beimplemented at least in part by means of the signal processor DSP ore.g. also by means of the above-mentioned microcomputer 55. The creationand implementation of corresponding algorithms, which correspond withthe aforesaid equations or which emulate the functioning of theamplitude regulating circuit 51, respectively the frequency regulatingcircuit 52, as well as their translation into program code executable insuch signal processors, is familiar per se to those of ordinary skill inthe art and, thus, does not, at least when knowing the presentinvention, require any detailed explanation. Of course, theaforementioned equations can also be easily represented totally orpartially in the measuring device electronics 50 by means ofcorresponding, discretely constructed, analog and/or digital calculatingcircuits.

In a further development of the invention, the instantaneously suitablecorrection value X_(K) is determined practically directly duringoperation, starting from the intermediate value X₂, by mapping,especially programming, in the measurement device electronics a uniquerelationship between the current intermediate value X₂ and thecorrection value X_(K) matched thereto. To this end, the measuringdevice electronics 2 has a table memory, in which a data set isinitially stored, for example in the form of digital correction valuesX_(K,i) determined during the calibration of the Coriolis mass flow ratemeasuring device. These correction values X_(K,i) are directly accessedby the measuring circuit via a memory address derived by means of theinstantaneously valid, second intermediate value X₂. The correctionvalue X_(K) can e.g. be determined in simple manner by comparing theinstantaneously determined intermediate value X₂ with correspondingdefault values for the intermediate value X₂ entered in the table memoryand reading out, and thus using from the evaluation electronics 2 forthe further calculation, that correction value X_(K,i) that correspondsto the default value coming closest to the intermediate value X₂.Serving as table memory can be a programmable, read only memory, thus aFPGA (field programmable gate array), an EPROM or an EEPROM. The use ofsuch a table memory has, among others, the advantage that the correctionvalue X_(K) is very rapidly available during run time followingcalculation of the intermediate value X₂. Furthermore, the correctionvalues X_(K,i) entered in the table memory can be initially determinedvery accurately, e.g. based on the Equations (2), (3) and/or (4), and byapplication of the method of least squares.

As is evident on the basis of the above explanations, a correction ofthe intermediate value X′_(m) can be carried out using fewer, verysimply determinable, correction factors. On the other hand, thecorrection can be performed using the initially determined viscositymeasurement value X_(η), and the initially determined intermediate valueX′_(m), with a calculation burden small in comparison to the initiallymentioned, more complex calculational method. An additional advantage ofthe invention is that at least some of the aforementioned correctionfactors can be derived without difficulty from the flow parametersdetermined by means of Coriolis mass flow rate measuring devices,especially from the measured density and/or the—hereprovisionally—measured mass flow rate, and/or from the operationalparameters usually directly measured in the operation of Coriolis massflow rate measuring devices, especially the measured oscillationamplitudes, oscillation frequencies and/or the exciter current itself.

While the invention has been illustrated and described in detail in thedrawings and forgoing description, such illustration and description isto be considered as exemplary not restrictive in character, it beingunderstood that only exemplary embodiments have been shown and describedand that all changes and modifications that come within the spirit andscope of the invention as described herein are desired to protected.

1. A Coriolis mass flow measuring device for measuring the mass flowrate of a medium, said medium flowing in a pipeline and said mediumincluding a first phase and a second phase, said Coriolis mass flowmeasuring device comprising: a vibratory transducer, said vibratorytransducer including at least one measuring tube to be interposed in thepipeline for guiding the medium to be measured, an exciter arrangementacting on said at least one measuring tube for causing said at least onemeasuring tube to vibrate, and a sensor arrangement for registeringvibrations of said at least one measuring tube and for generating afirst oscillation measurement signal representing oscillations of saidat least one measuring tube at the inlet end and for generating a secondoscillation measurement signal representing oscillations of said atleast one measuring tube at the outlet end; and measuring deviceelectronics electrically coupled to said vibratory transducer, saidmeasuring device electronics delivering an exciter current for drivingthe exciter arrangement, and said measuring device electronics producinga correction value based on a viscosity of the medium and an apparentviscosity derived from said exciter current, wherein the measuringdevice electronics uses said first and second oscillation measurementsignals and said correction value to produce a mass flow ratemeasurement value representing a mass flow rate to be measured.
 2. Amethod for measuring a mass flow rate of a medium, said medium flowingin a pipeline and said medium including a first phase and a secondphase, said method comprising steps of: flowing the medium to bemeasured through at least one measuring tube of a vibratory transducercommunicating with the pipeline; feeding an exciter current into anexciter arrangement mechanically coupled to the measuring tube guidingthe medium and vibrating said at least one measuring tube; registeringvibrations of said at least one measuring tube and producing a firstoscillation measurement signal representing inlet-end oscillations ofsaid at least one measuring tube and a second oscillation measurementsignal representing outlet-end oscillations of said at least onemeasuring tube; producing a correction value based on a viscosity of themedium and an apparent viscosity derived from said exciter current, andusing said first and second oscillation measurement signals and saidcorrection value to produce a mass flow rate measurement valuerepresenting a mass flow rate to be measured.
 3. A method for measuringa mass flow rate of a medium including a first phase and a second phase,said method comprising steps of: flowing said medium through at leastone vibrating measuring tube; producing a first oscillation measurementsignal and a second oscillation measurement signal, each of said firstand second oscillation measurement signal representing oscillations ofsaid at least one measuring tube; producing a first intermediate valuecorresponding to a phase difference between said first and secondoscillation measurement signals, producing a second intermediate valuecorresponding to an apparent viscosity, determining a viscosity of themedium; and producing a mass flow rate measurement value representing amass flow rate to be measured based on said first and secondintermediate values and said viscosity of the medium.